Abirth defect (orcongenital disorder) is a defect in ababy at birth, or which develops in the first month of life.[2]
The term isneutral as to whether the cause isgenetic (inherited birth defect) orenvironmental (causes in the environment, that is,outside thefoetus). If a condition is said to be "congenital", that is neutral language. Often it is not known what causes a condition found at birth. In common use, it is often redirected to "birth defect". That term is also neutral as to cause.
There are two main types of congenital defect. The first is caused bygenetic abnormalities, which arehereditary. The second may be caused by conditions (such asinfectious diseases) which a baby may get.[3] However, we may not know what caused the condition.
Sometimes doctors may find out that a baby has a congenital disorder before its birth. They useprenatal diagnosis andscreening tests, such asamniocentesis.[4]
Somegenealleles (versions of a gene) can damage the baby.
Conditions likedwarfism are nearly alwaysgenetic in origin. One type,achondroplasia, happens when a child'sbones does not grow correctly. Another type is caused bypituitary malfunction, where the pituitarygland, which puts out growthhormones, does not work properly.[5]
Manygenetic disorders are caused bymutations (or changes) in genealleles. Mutations can cause development to go wrong, or a simplebiochemical deficiency (the body does not have enough of an important chemical). In the case of a chemical deficiency, the problem may be curable. For example,phenylketonuria was a cause ofmental retardation. Doctors came up with a simple test to find which babies have this condition. They found that if these children got treated and followed a strict diet, they could get enough of the chemical they needed. Phenylketonuria now causes few cases of mental retardation.
Cellsdivide and copy themselves to producegametes. Sometimes, errors happen in the way thatchromosomes are copied during this process. These errors are then copied again and again as cells keep dividing and copying themselves. The most common chromosomal disorder isDown syndrome ('Mongolism'). This condition happens when a child has three copies of the 21st chromosome, instead of two.
The other main type of congenital disorder is caused by aninfectious disease being passed from mother to child. For example, If apregnant woman getsrubella, her child can have many birth defects. Congenitalsyphilis was common a century ago, and congenitalAIDS occurs today, and is common in some parts ofAfrica.
Screening andantibiotics has caused the number ofinfections transmitted by the mother to drop. It is a much smaller proportion than a century ago, despite AIDS. Also, maternalnutritional defects are much rarer, except in countries where food supply is limited. Therefore,genetic disorders have grown as a proportion of the total congenital defects.
Sometimes mothers take chemicals which cause theembryo damage.[6] Any substance that causes birth defects is known as ateratogen.
Drugs taken by the mother may affect development of theembryo. Pregnant women are not allowed to use some drugs. For example,thalidomide should not be used by a pregnant woman, or it can cause many defects in thefoetus.
If the mother took certain things during pregnancy, these can lead to problems with the baby. Common examples of such things are smokingtobacco, or drinkingalcohol.Food related: Pregnant women should eat well. If a pregnant woman does not receive enoughfolic acid with her food, the child can getneural tube defects.
Many women give upcigarettes andalcohol whenpregnant, because this gives the embryo a better chance of developing normally.[7]
About 3 percent of all babies have what is called amajor physical anomaly. This is something that damages the way the baby looks, or how it functions (itsphysiology).[8]
Birth defects involving thebrain are the most common problems. They concern about 10 per 1000 live births, compared toheart problems, at 8 per 1000,kidney problems at 4 per 1000, andlimbs at 1 per 1000. All other physical anomalies together occur in 6 per 1000 live births. The human brain has had changes and expansion fairly recently in evolutionary terms.
Birth defects of the heart have the highest risk of death during childhood. They are the cause of 28% of infant deaths due to birth defects.chromosomal abnormalities andrespiratory abnormalities each account for 15%, and brain malformations about 12%. About 10% of deaths in children are because of agenetic disease. This is (in modern times) more than the number of deaths caused byinfectious diseases.[3]
China Birth Deformity Monitoring Centre says that one baby with birth defects is born every 30 seconds in China.[9]
Pregnancies which do not come to term (miscarriages) have similar causes to birth defects. Many will be due to failures in the genetics controlling development of theembryo.
Most clinically apparent miscarriages (two thirds to three-quarters in various studies) occur during the first trimester.[10][11] Chromosomal abnormalities are found in more than half of embryos miscarried in the first 13 weeks.
A pregnancy with a genetic problem has a 95% probability of ending in miscarriage.[12] Genetic problems are more likely to occur with older parents; this may account for the higher miscarriage rates observed in older women.[13]
{{cite book}}: CS1 maint: location (link) CS1 maint: numeric names: authors list (link){{cite book}}:Unknown parameter|authors= ignored (help){{cite web}}:More than one of|archivedate= and|archive-date= specified (help);More than one of|archiveurl= and|archive-url= specified (help){{cite journal}}: CS1 maint: numeric names: authors list (link){{cite web}}:More than one of|archivedate= and|archive-date= specified (help);More than one of|archiveurl= and|archive-url= specified (help)CS1 maint: numeric names: authors list (link){{cite web}}: CS1 maint: numeric names: authors list (link){{cite journal}}: CS1 maint: numeric names: authors list (link){{cite web}}:More than one of|archivedate= and|archive-date= specified (help);More than one of|archiveurl= and|archive-url= specified (help) taken word-for-word from pp. 347-9 of:"Chapter 27. What to do when miscarriage strikes".The PDR Family Guide to Women's Health and Prescription Drugs. Montvale, NJ: Medical Economics. 1994. pp. 345–50.ISBN 1-56363-086-9.